Method of making spark gaps and products thereof



April 20, 1948;` E QLES y 2,440,153y METHOD OF MAKING SPARK GAPS ANDPRODUCTS THEREOF Filed'July 4, 1945 INVENTOR ATTORNEY Patented Apr. 20,"1948 METHOD F MAKING SPARK GAPS AND vPRODUCTS THEREOF Herbert E. Oles,Indianapolis, Ind., assigner to P. R. Mallory & Co., Inc., Indianapolis,Ind., a

corporation of Delaware Application July 4, 1945, Serial No. 603,203

Claims. l

The present invention relates to spark gaps or impulse gaps and to anovel method of making such gaps.

Spark gaps or impulse gaps are used at present for various applications,of which the principal one is their use in high frequency ignitionsystems. In general, such gaps comprise two spaced electrodes which areconnected in an electric circuit capable of building up a high voltagebetween the electrodes so as to produce a spark discharge between thesame. The spark di..- charge may be used to produce high frequencyoscillations in a work circuit and for othery purposes. Spark gaps ofthe described character are disclosed, for example, in Patent Number2,354,- 786 grantedtofAlexander C. Wall on August 1, 1944, and also in aco-pending application of Alexander C. Wall and Herbert E. Gles, SerialNo. 582,136, led on March l0, 1945.

It is an object of the present invention to improve the characteristicsof spark gaps or impulse gaps of the described type.

It is another object of the invention to provide a method of producingspark gaps having eX- tremely stable characteristics and particularlyhaving a very stable break-down voltage.

(ciers-a5) I the ends of which are inserted into the annular' Other andfurther objects and advantages ofthe invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawing; in which Figure l is a longitudinal sectional view of a sparkgap embodying the invention during the process of its manufacture;

Figure 2 is a circuit diagram of a typical impulse circuit employed incarrying the principles of the invention into practice; and

Figure 3 is a sectional View of the finished spark gap embodying theinvention.

Referring now to Figure 1 of the drawing, reierence numeral I0 denotes agap electrode of a generally circular shape constituted of a suitablerefractory metal, such as, for example, tungsten. This electrode isbrazed or otherwise mounted on a cup-shaped electrode holder plate I i.A n end plate I2 is welded to flange I3 of holder plate II and isprovided with a U-shaped annular channel It.

Electrode l0, holder plate II and-end plate I2 constitute an electrodeassembly. This assembly is mounted together with another assembly oiidentical character so that the two electrodes of the respectiveassemblies are held in parallelspaced cooperating position. This isaccomplished by means of a spacer tube I5 of glass or some othermaterial of an insulating character,

channel I4 of the end plates. Preferably, end plates I 2 are constitutedof a suitable ironchromium alloy which may be directly sealed to glassthereby providing a stable and hermetically sealed construction. Theinner space surroundingthe electrodes and dened by end plates I2 andspacer tube I5 is initially in communication with the externalatmosphere through openingsv or ports i6 provided in the electrodeholder plates II and through openings I'I in the center portion of theend plates I2. One of the openings I'I may be sealed by means of a glassbead I 8 while the corresponding opening Il of the other endplate has aglass tube I9 sealed thereto and provides a channel or duct through'which the inner space of the gap may communicate with the externalatmosphere. As spark gaps of the described character and the method ofmaking the same are fully disclosed in the said co-pending applicationSerial No. 582,136, no detailed description of the construction of thegap will be necessary.

I have discovered that the operating characteristics of a gap of thedescribed character may be greatly improved by means of a specialconditioning treatment after the structural completion of the gap andprior to applying the nal seal thereto. This treatment comprisesconnecting the gap in a typical impulse circuit which periodicallyapplies high voltages to the electrodes of the gap. The impulsegenerating circuit may comprise a suitable source of electrornotiveforce, such as a conventional ignition magneto. The wave form generatedmay be such that it has approximately a 1000 cycle rate of rise and theoutput may be approximately 2000 volts peak when connected across a .015microfarad condenser without the gap. The Work circuit may comprise atypical lead and spark plugv operating in a bomb containing nitrogen, orsome other suitable inert gas, with fifty pounds pressure on the nose ofthe plug. The application of these periodically acting impulses may becarried on for an extended period such as for twenty hours, or more. Ithas been found that if thegap is filled with a suitable gas after thistreatment and sealed, a spark gap of superior operating characteristicsand of greatly increased stability is obtained.

The invention will now be more fully described in connection with Figure2 in which a typical impulse circuit is diagrammatically shown.Thecircuit comprises a magneto, generally denoted by reference numeral20. The magneto includes a primary winding 2| and a secondary winding22, which are inductively coupled to each other. One end of bothwindings is grounded and a condenser` 23 is connected across primarywinding 2l. The magneto also includes a pair of interrupter contacts 24operated by means of a rotary cam 25.

Another condenser 25 yof suitable capacity is connected across secondarywinding 22 of the magneto. The spark gap to be treated, includ'- ingelectrodes Il) and diagrammatically shown as element 21, is connectedbetween the .common terminal of secondary winding 22 and condenser 26,and one end of primary winding 28 of a step-up transformer. The `otherend `of said winding 28 is grounded. Primary winding Z5 is inductivelycoupled with secondary Winding 23 of the step-up transformer one end oiwhich is connected to the center terminal Se of a spark plug 3l. Thisspark plug is inserted into a pressure-resistant container or bomb 32.The bomb may be iilled with a suitable gas, such as nitrogen, under apressure of fifty Vpounds per square inch, in order to simulate theoperating conditions within the cylinders of fan internal com-- bustionengine.

In carrying outthe method `of the-invention, the spark gap 2l to betreated is connected into the 'impulse circuit of vFig-ure 2. 1n orderto olotainnthe desired resultsyit is 'essential that the gaseousproducts of the presparking treatment be continuously removed from theinteriorof 'the spark gap. In the simplest case, this may be accomplished by maintaining the interior of the gap `communication withthe atmosphere through ports Iii and I1 and glass tube I9 4(liig. l). It4is also possible, however, to pass -a flow of a. filtered and cleanedgas, 4such as airfthrough the gap., said flow being introduced throughtube ISiand withdrawn or discharged through port Vifi before it issealed at I8.

IDuring the operation of vthe magneto, a high `voltage, as described, isperiodically built up across condenser 26. .After this voltage hasreached the break-down voltage of gap A2l, an oscillatory discharge willtake placethrough'said gap and through primary winding 280i the :stepuptransformer. An oscillatory current of similar high frequency buto'fconsiderably higher voltage will be built up across secondary winding2-9 and willlproduce high frequency sparks between-center electrode 30and electrodes 33 of spark plug 3i.

This presparking treatment is `preferably continued for an extendedperiod `of time'such as for twenty to Vforty hours. `In general, apresparking treatment for approximately twenty hours at Aabouttwenty-two sparks per second has been found to providevsatisiactoryresults.

After the presparkingtreatment has been completed, the spark gap may beevacuated, 'filled with a suitablegaseous charge, and Yis hermeticallysealed. Excellent results, however, 'have been obtained by sealingthespark 4gap immediately after the presparkin'g treatment without'fapreliminary evacuation process. nfthat'case, the inner space of thegapwill be lled 'with a gaseous charge having a composition which issubstantially identical with that of atmospheric air, that is, it willcontain approximately 21 per cent of oxygen, 79 per cent of nitrogen and'traces'of certain noble gases foundin 'small quantities in atmosphericair,'such as helium, neon, argon, krypton and' xenon. This charge willbe under normal atmospheric pressure, corresponding to the pressure vatthe time of Asealing thegap.

The finished gap is illustrated in Figure 3 and is in every respectidentical with that shown in Figure 1, except that glass tube I9 hasbeen sealed off close to the lower end plate, constituting a glass bead34 similar to glass bead I8 sealing the upper end plate.

Experience has demonstrated that lasspark gap produced in accordancewith the principles of the present invention provides importantadvantages. Thus, the spark gaps made by the method of the inventionpossess extremely stable physi- 'cal characteristics. For example, thevoltage neofe'ssary to produce a discharge between the electrodes willvary only as little as five per cent or less. Moreover, spark gapsprepared according 4tothe invention will retain their desirable physicalcharacteristics for a very long time and as a result, Vhave a very longuseful life.

The physical principles underlying the descried presparking treatmentand responsible for the lgreatly improved operating characteristics cithe gaps treated in accor-dance with the inven tion are not fullyunderstood. It is believed that during the presparking treatment minutebut critically important changes are caused in the electrode surfaces,while the gaseous and solid try-products of the treatment are removedfor example by permitting them to escape into the atmosphere. Therefore,any possible initial changes in the physical characteristics of theelectrodes and of the gap will already occur during the presparkingperiod which is continued until such characteristics are permanentlystabilized. While this explanation appears to be well supported by`experimental evidence, the vinvention is, of course, independent fromthe merits of Iany theoretical consideration.

Although the present invention has been disclosed in connection with apreferred embodiment thereof, variations and modifications may beresort-ed to by those skilled in the art without departing from theprinciples of the invention. I consider all of these variations andmodifications to be within the true spirit and scope of the presentinvention, as disclosed in the foregoing description, and vdeiinedby theappended claims.

What is claimed is:

1. The method of making impulse gaps of Ystable characteristics whichcomprises providing a pair of spaced plane electrodes constituted ofrefractory metal within a gas-tight container, maintaining saidcontainer in communication with the external atmosphere, presparkinglsaid electrodes for a period of several hours, and then hermeticallysealing said container.

2. The method of making impulse gaps of stable characteristics whichcomprises providing a pair of plane parallel-spaced tungsten electrodeswithin a vessel adapted to be hermetically sealed, initially maintainingthe interior of said vessel in communication with the externalatmosphere, connecting said electrodes to an impulse circuit toproduce aplurality 'of electric sparks per second between said electrodes for aperiod'of several hours, a-nd hermetically -sealing said Vessel aftersaid sparking period thereby to obtain an impulse gap of stableoperating characteristics.

3. The method of making impulse gaps of stable characteristics whichcomprises providing a pair of parallel-spaced circular tungsten electrodes within a vessel adapted to be hermetically sealed, maintainingthe gaseous atmosphere within said vessel in communication with theexternal atmosphere, connecting said electrodes to an electrical impulsecircuit to produce electric sparks in the order of about twenty sparksper second for a period in the order of about twenty to forty hours, andhermetically sealing said vessel after said sparking period thereby toobtain lan impulse gap of stable operating characteristics.

4. The method of making impulse gaps of the type including a pair ofspaced electrodes within a sealed vvessel which comprises establishingcommunication between the interior of said vessel and the externalatmosphere, presparking said electrodes for a predetermined period whilemaintaining such communication, and then hermetically sealing saidvessel.

5. An impulse gap of stable characteristics comprising a hermeticallysealed vessel, a. gaseous atmosphere in said vessel having a compositionsimilar to that of the external atmosphere, and a pair of planeelectrodes constituted of refrac- 6 tory metal mounted in said vessel inparallelspaced position, said electrodes having surfaces of suchphysical characteristics as is obtained by presparking them for anextended period.

HERBERT E. CLES.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,879,131 Dobke Sept. 27, 19321,933,329 Hull Oct. 31, 1933 1,965,584 Foulke July 10, 1934 2,199,866Alterthum May 7, 1940 2,288,861 Watrous July 7, 1942 2,300,931 KalischerNov. 3, 1942

